Not sure if this exactly falls under green building, but didn't know which section was best.

I have a pretty decent well and I would like to be able to use it interchangeably with the mains water (which isn't particularly reliable in my village anyway and often runs dry towards the end of the summer - this year there were 3-4 months with no rain). The well is pretty good, though, so I'd like to be able to use that primarily, with the option to switch to the mains if needs be.

Does anyone have any experience rigging up wells? I'd probably use an external pump with attached pressure tank (50lt) but what about things like pressure regulators and filters to stop sand screwing up the pump and the water heater? Any advice would be warmly receiveved.

I didn't answer this earlier because I have no experience of sand in well water, my well is bored through slate.

As far as pumping, it depends to a certain extent on the depth of your well. Mine is a bore hole and I think (if I remember rightly) is about 130 feet deep and I have a submersible pump down the bottom with a pressure vessel at the top controlled by a pressure switch that keeps the tap pressure at a steady(ish) 2 bar.
On a shallower well you have the option of having the pump at the top of the well, which amongst other things means a cheaper pump.
But if you have sand in your water, you will be replacing pumps on a very regular basis and I don't think you could install a filter before the pump and even if you could, it would involve a lot of work regularly changing or cleaning the filter element.

If you have a shallow well, then I think the answer might be to use a diaphragm pump that delivers the water to a settlement tank and then feed the (sand free) outflow to your house, either by gravity if you can arrange it or by a pressure controlled pump.
Diaphragm pumps have no moving metal parts in contact with the water so would survive being "sand blasted" and you can replace the diaphragm and valves when they eventually wear out.

The well is a regular old-fashioned one, about a metre in diameter with bucket and chain and all that. The surface of the water is about 4-5m down at the moment, although we have just come to the end of a 3-month draught so it might be higher normally. I lowered the bucket down as far as the chain would allow it, which I guestimated to be about 15m long, and it didn't touch the bottom. There is already a pipe which goes down into the well and out to a pump housing next to the well, and then across to the utility room under the house, where another pipe goes up to the bathroom. They did once have it rigged up, but the previous occupants stripped everything out: shower unit, sink, WC, pump, pressure tank, etc. As a result, I have no idea what system they used and how effective it is. As a result, I was planning just to start from scratch.

I'm pretty sure that there will be sand in the bottom of the well although I might be lucky enough to rarely suck any up. When I take a bucket of water out of the well, there is a small amount of sediment floating around in it, especially if I drop the bucket quite a way under the surface. How adversely that'll affect pump operation I cannot really say, and that's my problem - I know didley about pumps and wells. I'm more than happy to fit a WC or a sink, but getting the water there is something new to me.

Those kinds of pumps are generally readily available here and a lot cheaper. That one in the pic seems to be quite a powerful one but I'd only need to raise the water about 8-9m to get the job done.

To avoid liability issues, you should put a back-flow preventer (one-way valve) on the mains at a point before it jpoins the flow from the well. That will prevent any possibility of well water getting into the mains, should you ever have a contamination issue.

Just to update: Most people I spoke to suggested using a submersible pump for the well because of the depth so that's what I'm going to install. This will draw the water up to a 100l expansion tank with pressure gauge, pressure switch, filter and valve. I might connect it up to the main too one day, but for the moment I'll just use the well water and see how that goes. If I connect to the mains, I'll be sure to add a back-flow preventer (cheers Keith).

Due to lack of plumbers in the area, I'm going to install the pipework myself. I've drawn up a schematic and had it ok-ed by a plumber here in the capital. I've opted for pex-al piping as that seems to be the easiest for the amateur to install, has a reportedly good resistance to freezing, and doesn't require any expensive tools. I've started preparing the bathroom but don't really want to start running pipes until I've had the walls plastered, something I'm definitely not going to try myself - I do want them reasonably straight!